HP 83751A User Manual page 178

Special Functions
for a chosen span and meet all specihcations. The sweep tune is limited by a
400 MHz/ms sweep rate.
When sweep time auto is "on,"the fastest sweep tune allowed for the
frequency span swept is automatically selected. When sweep tune auto is
"off," changing frequency span does not change the sweep time.
SWEep:TIME:AUTO
SWEep:TIME:AUTO
15-8
Associated SCPI Commands
ON
Turns off sweep time Auto.
OFF